IMHO you translated it wrongly in the other part. These sopravvenienze attive is income that you have suddenly discovered that you earned the year before. It is a bit unusual to add the adjective "straordinarie" to them, but I can't see any alternative but to add "extraordinary" to it. Possibly because they relatively big.

http://it.wikipedia.org/wiki/Sopravvenienze_attive

Le sopravvenienze attive sono componenti positive del reddito che derivano da costi ed oneri sostenuti in esercizi precedenti e vengono meno in un determinato esercizio. Si considerano sopravvenienze attive: 1) spese, perdite ed oneri dedotti in precedenti esercizi 2) ricavi o altri proventi conseguiti di ammontare superiore a quelli che hanno formato il reddito in esercizi precedenti 3) ricavi o la sopravvenuta insussistenza di oneri e spese riportati in esercizi precedenti



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Note added at 54 mins (2012-03-02 19:53:19 GMT)
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Looked at your link. Yes "straordinario" is big and not recurring, but may be caratterisco (core business) however. There is a huge amount of hair-splitting in there which only really becomes important when it is tax related. The important thing about using "prior year income" is that it is clear that it is recognised this year i.e. in this year's income statement (or explanatory table for it). That way you can see it is an exception, because everything else was this year. It isn't usually a problem though.